1. Field of the Invention This invention relates to a polypropylene resin composition. More particularly, it relates to a polypropylene resin composition, having mouldability which can provide moulded articles superior in rigidity, impact resistance and resistance to sink mark forming, if moulded articles are made therefrom.
With regard to the materials for interior automotive trims, appliance parts, parts of office automation machineries, etc. tendency of utilization of plastics is increasing lately, particularly from the viewpoint of their light weight and economical advantage. Among them polypropylene resin which is superior in moldability, economical aspect, appearance and shape, mechanical strength, resistance to climate (weatherability) and durability of moulded product, is desirably used.
However, interior automotive trims or appliance parts, etc. which are moulded by using conventionally known polypropylene resin have drawback because they have latent residual stress due to inner strain caused during the process of cooling after moulding and on this account, when an article using these parts is exposed to the atmosphere at a temperature of 70.degree.-12.degree. C. at the time of practical use, release of internal stress occurs, resulting in secondary deformation of the articles to which these parts are attached and losing value as articles of commerce. Further sink marks formed by shrinkage due to cooling process after moulding, bring about defect in spoiling the appearance of moulded articles.
In order to overcome these drawbacks, polypropylene to which an inorganic filler is incorporated, a so-called inorganic-filler-containing polypropylene resin is being used abundantly now. However, the use of such an inorganic-filler-containing polypropylene resin may improve the secondary deformation and sink mark forming but causes drawback in the point of lowering of impact strength of moulded articles and makes moulded articles brittle.
We, the inventors of this invention have made strenuous effort in study to improve the drawbacks of the above-mentioned polypropylene resin composition. As the result, to be astonishing enough, we have found that a composition formed by blending a prescribed amount of organic fibers or a prescribed amount of organic fibers and an inorganic filler with propylene-ethylene block copolymer modified with an unsaturated carboxylic acid or its derivative have good moldability and when it is made into moulded articles, it provides moulded articles superior in rigidity, resistance to impact, and to sink mark forming and based upon this finding, we completed the present invention.
As evident from the foregoing description, the object of the present invention is to provide a polypropylene resin composition, having good moldability which can produce a shaped articles, superior in rigidity, impact resistance and capability of prevention of sink mark forming.